PASADENA, Calif. (AP) _ Some of the most cracked, squeezed and stretched landscape yet seen on Venus has been captured in pictures made by the Magellan spacecraft, now halfway through its $744 million mission.

The planet's Alpha Regio volcanic highland ''is an area that looks really tortured,'' said Steve Wall, Magellan experiment representative at NASA's Jet Propulsion Laboratory.

Brown University scientist Annette deCharon said that Alpha Regio's faults, mountain ridges and valleys constitute ''some of the most complicated terrain we've seen in Magellan data.''

The highland, a region where Venus' crust is unusually thick, now apparently is being stretched apart, possibly as it slumps toward surrounding lowlands, she said. Some of its valleys are filled with solidified lava flows.

Wall, deCharon and laboratory scientist Richard Goldstein displayed the pictures Wednesday on NASA closed-circuit television after Magellan passed the halfway point in its eight-month primary mission. No prints of the pictures were released.

The polar-orbiting spacecraft's mission is to use radar to make pictures of 70 percent to 90 percent of Venus' cloud-covered surface as the planet slowly rotates once on its axis. That takes 243 Earth days.

By Wednesday morning, the spacecraft had flown over 50.9 percent of the Venusian surface and successfully made pictures of 41.4 percent of the terrain, Wall said.

The 50.9 percent of Venus over which Magellan has flown equals an area that on Earth would stretch from Los Angeles east to Bombay, India, and from the North Pole to the southern tip of South America, Wall said.

On Wednesday, Magellan was mapping Aphrodite Terra, a continent-like highland the size of Africa that straddles Venus' equator. It earlier flew above Alpha Regio, an 800-mile-wide highland that rises one-half mile to 1.9 miles above surrounding southern hemisphere lowlands.

There are several theories to explain formation of the Alpha highlands, including massive floods of erupting lava, squeezing of the planet's crust and the kind of slow, linear volcanic eruptions that happen along Earth's midocean ridges, where new crust is created and added to giant drifting plates of rock.

There is no obvious evidence that Venus has such plate tectonics, also known as continental drift, deCharon said.

The National Aeronautics and Space Administration launched Magellan from space shuttle Atlantis on May 4, 1989.

It began orbiting Venus last Aug. 10 and started its formal $744 million mapping mission Sept. 15 after a monthlong delay caused by a glitch that made the spacecraft temporarily lose contact with Earth.